Patients with primary biliary cirrhosis suffer from severe bouts of itching, which is manifested by chronic scratching. In order to evaluate the efficacy of experimental drugs that may relieve the itching, it is necessary to quantify the scratching. A piezoelectric foil cemented to the patient's primary scratching fingernail transduced mechanical vibrations, generated by the scratching, into an electrical signal applied to the input of a miniature FM transmitter. After the signal was obtained with an FM receiver, it was processed by a custom-designed frequency counter, which in turn was interrogated and reset periodically by a personal computer. The study consisted of measurement periods of six to eight hours, both before treatment and after treatment with specific drugs. Each patient served as his or her own control.